Vacuum interrupter

ABSTRACT

A high voltage, high current vacuum fuse having a pair of conductive members supported in a spaced relation within a dielectric housing and shielded by a condensation shield, the conductive members being interconnected either by a fusible link or by a conductive element and a pair of fusible links, the fusible link or links being of a minimum volume and the conductive members being spaced to provide a gap of sufficient length to interrupt current. The conductive members or the element being biased to increase the gap on fusing on the fusible link.

United States Patent [191 Link 11] 3,806,680 [451 Apr. 23, 1974 VACUUM INTERRUPTER Edwin A. Link, 317 S. Greenfield Ave., Waukesha, Wis. 53186 Filed: Oct. 21, 1971 Appl. No.: 191,205

Related US. Application Data Continuation-in-part of Ser. No. 18,868, March 12, 1970.

Inventor:

[52] US. Cl. 200/144 B, 337/405, 337/152, 7 337/l66, 337/410, 337/248 Int. Cl. H0lh 33/66 Field of Search 200/144 B; 337/405, 410,

[56] References Cited UNITED STATES PATENTS 7/1896 Woolley 337/405 6/1907 Simons 337/410 10/1952 Laing 337/166 X [0/1954 Laing et al.... 337/166 X l2/l955 Von Hoorn... 337/166 X 9/1956 Van Eyk 337/152 X Sims et al 337/405 UX 3,190,986 6/1965 Jennings 337/248 3,386,063 5/1968 Mansfield, Jr. 337/405 X 3,436,712 4/1969 Heaney 337/405 FOREIGN PATENTS OR APPLICATIONS 574,023 4/1959 Canada 337/166 l77,384 12/1935 Switzerland... 337/410 Primary ExaminerRobert S. Macon Attorney, Agent, or Firm-Ronald E. Barry [5 7] ABSTRACT 9 Claims, 5 Drawing Figures I" ll t Ill I'll lll -t 1 VACUUM INTERRUPTER RELATED APPLICATION BACKGROUND OF THE INVENTION Vacuum fuses generally have been provided with a fusible link throughout the full length of the fuse connected to conductive members at each end of the fuse. A condensation shield is often provided around the fusible link to mask the inside surface of the dielectric housing and prevent the vaporized fuse link material from depositing on the inside surface of the housing thereby preventing flash-over between the conductive members. However, it has been found that due to the large mass of the fusible element, the vapor pressure produced on fusing of the element is large enough to produce an arc plasma sufficient to support an are long enough to cause an explosive condition in the fuse.

SUMMARY OF THE INVENTION The vacuum fuse of the present invention minimizes the amountof material in the fuse link while still providing a sifficient gap between the conductive members to interrupt current. The reduced amount of fusible material which can be vaporized and the establishment of a gap between the conductive members assures immediate interruption of current. This can also be achieved by supporting an electrically conductive element on a pair of small fusible links in the gap provided between the conductive members. On fusing of the small links, the large movable element will drop out of the gap in the conductive members leaving a gap of sufficient size to prevent arc-over. The movable element can be supported on atorsion spring which is biased to move the movable element to a neutral position relative to the conductive member on fusing of the fusible link.

In another embodiment of theinvention, a pair of conductive members having a substantially large mass are supported in a spaced relation within the housing with a single fusible link interconnecting the stationary members. The mass of the conductive members provided a cooling surface immediately adjacent the fusible link for condensing the vaporized fuse material. The immediate condensation of the vaporized fuse material minimizes the possibility of establishing an are plasma between the conductive members which could prolong the time of arc interruption.

THE DRAWINGS Flg. 3 is a side view in section of a modified vacuum fuse;

FIG. 4 is a side view in section of another form of the invention having a single fusible link interconnecting stationary conductive members having an enlarged head at the end; and

FIG. 5 is a side view in section of another embodiment of the invention showing a single fusible link conmeeting a stationary conductive member to a movable conductive member.

DETAILED DESCRIPTION OF THE DISCLOSURE The vacuum fuse of this invention is shown in FIGS. 1 and 2 as a one shot type fuse 10 as generally used in a high current, high voltage network. The fuse 10 generally includes a hollow, cylindrical housing 12 formed of a dielectric material such as procelain or glass, a cylindrical condensation shield 14 having flanges 15 secured to the housing 12 and conductive members 16 supported within the housing 12 by means of end walls 18. The edges of the end walls 18 are hermetically sealed to the housing 12 and the conductive members 16. Circuit interruption is achieved by fusing links 24 connected to the conductive members 16 within the condensation shield 14 to produce a gap 23 of sufficient width to prevent arc-over.

In accordance with one aspect of the invention, means are provided for producing the gap 23 between the conductive members 16 under overload or fault current conditions by fusing only a small portion of fusible material. Such means includes a movable element or disc 22 supported in the gas 23 between the conductive members 16 by a pair of small fusible elements or links 24, The disc 22 and the links 24 can be formed as integral parts of the conductive members 16 or as separate parts secured to the conductive members 16. The disc 22 normally lies in a plane generally parallel to the longitudinalaxis a of the conductive members 16. When an overload occurs in the line, the two small fusible links 24 will fuse leaving the disc 22 free to drop out of the gap 23 between the conductive members 16. The gap produced in the conductive members 16 by removing the disc 22 is of sufficient width to prevent areover.

The vaporized material of the links 24 is prevented from depositing on the inside surface of the housing 12 by means of thecondensation shield 14 which substantially completely condenses all of the vaporized material. More specifically, it should be noted that the links 24 are quite small so that a relatively small amount of material is vaporized when the links 24 are fused. This small amount of material will be completely condensed by the condensation shield 14. Little, if any, material will deposit on the inside surface of the housing thereby substantially eliminating the possibility of flash-over occurring across the inside surface of the housing 12.

Means are provided for supporting the disc 22 for movement from the normalor'conductive position parallel to the longitudinal axis a of the conductive member 16 to a neutral or non-conductive position transverse to the longitudinal axis 21" of the conductive member 16. Such means is in the form of a torsion spring 30 secured to the condensation shield 14 and to the disc 22. The spring 30 is normally twisted, as seen in Flg. l, to provide a bias for moving the disc 22 to the neutral position on release of the disc 22 from the conductive members 16. The space or gap between the conductive members and the disc or movable element 22 must be large enough to prevent arc-over when rotated to the neutral position.

Air is evacutaed from the housing by means of'a tube 35 sealed in an opening 36 provided in one of the end walls 18. Air is withdrawn from the housing by any conventional means to produce a vacuum and the tube 35 crimped and tinned to seal the housing. The end walls 18 and condensation shield 14 should be formed of a material having substantially the same coefficient of expansion as the housing 12. Kovar has been used for both the end walls 18 and the condensation shield.

The vacuum fuse can be formed by machining the two links 24 and the disc 22 as in integral part of the conductive member 16. The torsion spring 30 can be attached directly to the disc 22 or inserted into a slot provided in the disc 22 which is then pinched to secure the spring 30 in the disc. The ends of the torsion spring 30 are twisted and secured to the flange on one of the condensation shields 14. The housing 12 is initially formed in two sections, with the outer edges of the end walls 18 embedded in and hermetically sealed to the ends of the housing 12. The two sections of the housing 12 are hermetically sealed to the flanges 15 with the conductive member 16 projecting outwardly through the apertures 32 provided in the end walls 18. The flanges 15 on the condensation shield 14 are welded together with the ends of the torsion spring positioned between the flanges 15. A seal is provided between the end walls 18 and the conductive member 16 by silver soldering the edges of theend walls to the conductive member 16.

In FIG. 3 an alternate form of the invention is shown in which a unitary shield 40 is supported within a dielectric housing 42 by means ofan annular ring 44. The

ring 44 can be formed as an integral part of the housing 42, as a separate ring or as a number of independent segments all made of a dielectric material. The conductive members 46 are provided with a movable element or conductive disc 48 supported by fusible links 50. When the links 50 fuse, the movable member 48 will merely drop onto the shield leaving a gap between the conductive members 46.

Referring to FIG. 4 of the drawings, another embodiment of the invention is shown wherein a fuse hav-' ing a dielectric housing 52 and a cylindrical metallic shield 54 which acts as a condenser for metallic vapor and prevents the dielectric housing from being coated with metal. The housing 52 is closed at each end by end walls 58 to form a chamber within the housing 52 which is evacuated as described above. Conductive members 56 are supported in a spaced relation in the housing 52 by means of the end walls 58. The ends of each of the conductive members 56 are located in a spaced relation within the housing. The space or gap is closed to complete the circuit through the conductive,

members 52 by means of a fusible element or link 62.

relation to the fusible element 62 and thereby provide a large cooling surface on each side of the fusible element 62. When a short circuit current occurs, the fusible link 62 will vaporize and will immediately condense on the surface of the ends 60, and shields 54. In a high voltage application as contemplated here in, a cross-sectional area relationship between the ends 60 of the conductive members 56 and the fusible element 62 of five to one is required to provide sufficient cooling.

Immediate condensation of the vaporized fuse mate rial prevents the increase of vapor pressure within the housing 52. It should be understood that on vaporization of a fusible element an increase pressure occurs creating arc plasma sufficient to allow the arc to continue for more than one cycle. In order to achieve higher KV levels, it might be necessary to move one of the electrodes to increase the arc gap. In this regard another embodiment of the invention is shown wherein a fuse having a dielectric housing 72 and a metallic shield 74 in FIG. 5 is provided with a stationary conductive member 76 on one of the end walls 78 and a movable conductive member 80 supported by a tubular member 82 provided on the other end wall 84. The conductive members 76 and 80 have their inner ends 86 spaced a predetermined distance apart. The circuit through conductive members 76 and 80 is completed by means of a fusible element link 88 as described above.

The movable conductive member 80 is mounted on the tubular member 82, which is secured to the end wall 84 and is biased by means of a spring 80 toward the end wall 84. The conductive member 80 is connected into the circuit by means of a flexible electric line 92. The fuse of this embodiment is operated substantially in the same manner as FIG. 4. However, on fusing of the link 88 the spring 90 will move the member 80 toward the end wall 84. A dual function is thereby provided by the movable member 80, it provides a large cold mass to condense vaporized fuse material and increases the allowable KV recovery voltage determined by the anticipated KV in which the fuse is 6 to be used. For example, in a 15 KV system the fusible link 62 should have a length of approximately one-half inch. It should be noted that the ends 60 are massive in of the gap minimizing the possitilities for arc-over. Although a spring has been shown for biasing the conductive member 80, other types of biasing means can be used including the inherent resiliency of the conductive members. lclaim:

l. A one use high voltage vacuum fuse comprising a housing formed of a dielectric material,

to stationary electrically conductive members supported in a spaced relation within said housing and extending outwardly therefrom for connection to an electric circuit, a conductive bridging element, a pair of fusible links connecting said bridging elementto said stationary members, and means for supporting said bridging element for movement with respect to said stationary members whereby said bridging element is free to move to a position to form a gap on either side of said bridging element between said two stationary members when said links fuse, said gaps being of sufficient lengthto interrupt the circuit across the two stationary members. 7 2. A vacuum fuse according to claim 1 including a condensation shield supported within said housing in a position to mask said housing from said fusible elements.

fixed electrically conductive members adapted to be connected to an electric circuit,

an electrically conductive disc and a pair of electrically conductive fusible links connected between said disc and said fixed member, a housing formed of a dielectric material hermetically sealed to said fixed members to enclose said disc and said fusible links,

and means for biasing said disc for movement with respect to said fixed members whereby said disc is free to move on fusing of said links to provide a gap on either side of said disc between said fixed members of sufficient length to interrupt current flow.

7. The fuse according to claim 6 wherein said supporting means comprises a torsion spring for biasing said disc to a current interrupting position.

8. The fuse according to claim 7 including a condensation shield supported within said housing in a position to mask said housing from said fusible links.

9. The fuse according to claim 6 wherein said fixed members, conductive disc and fusible links are formed from a single piece of electrically conductive material. 

1. A one use high voltage vacuum fuse comprising a housing formed of a dielectric material, to stationary electrically conductive members supported in a spaced relation within said housing and extending outwardly therefrom for connection to an electric circuit, a conductive bridging element, a pair of fusible links connecting said bridging element to said stationary members, and means for supporting said bridging element for movement with respect to said stationary members whereby said bridging element is free to move to a position to form a gap on either side of said bridging element between said two stationary members when said links fuse, said gaps being of sufficient length to interrupt the circuit across the two stationary members.
 2. A vacuum fuse according to claim 1 including a condensation shield supported within said housing in a position to mask said housing from said fusible elements.
 3. A vacuum fuse according to claim 1 wherein said bridging member and said fusible links are formed as an integral part of said stationary members.
 4. A vacuum fuse according to claim 1 wherein said supporting means moves said bridging member to a position transverse to said stationary members.
 5. A vacuum fuse according to claim 1 wherein said supporting means comprises a torsion spring.
 6. A high voltage vacuum fuse comprising a pair of fixed electrically conductive members adapted to be connected to an electric circuit, an electrically conductive disc and a pair of electrically conductive fusible links connected between said disc and said fixed member, a housing formed of a dielectric material hermetically sealed to said fixed members to enclose said disc and said fusible links, and means for biasing said disc for movement with respect to said fixed members whereby said disc is free to move on fusing of said links to provide a gap on either side of said disc between said fixed members of sufficient length to interrupt current flow.
 7. The fuse according to claim 6 wherein said supporting means comprises a torsion spring for biasing said disc to a current interrupting position.
 8. The fuse according to claim 7 including a condensation shield supported within said housing in a position to mask said housing from said fusible links.
 9. The fuse according to claim 6 wherein said fixed members, conductive disc and fusible links are formed from a single piece of electrically conductive material. 